Abstract
  
Substitution of chemical additives by natural compounds is one of the current trends in the food industry. The design of film forming dispersions based on biodegradable biopolymers such as chitosan (CH) or hydroxypropylmethylcellulose (HPMC) in combination with natural antimicrobials appears as an innovative technology that can ensure the safety and prolong the shelf life of food. Essential oils present significant antimicrobial properties. Recent articles reported the large spectrum of action of these compounds, since they present an antimicrobial activity against different strains of fungi, yeasts, viruses and bacteria. Thus in the present study film forming dispersions (FFD) based on CH and HPMC with different concentrations of tea tree, lemon and bergamot essential oils were designed. The effect of the incorporation of these essential oils on the physicochemical properties of FFD and dry films and its diffusion in food simulants by gas chromatography were evaluated. The effect of the application of coatings based on CH, HPMC and essential oil of bergamot in the quality of grapes refrigerated was also studied. 
Results showed that the addition of essential oils in CH and HPMC resulted in significant changes in viscosity, particle size and ?-potential. All FFD showed pseudoplastic non-time dependant rheological behaviour. The addition of essential oils improved barrier properties to water vapour of CH and HPMC pure films.  Significant changes were also observed in terms of optical, mechanical and microstructure of films. Multivariate statistical analysis revealed a greater influence of matrix nature on the physicochemical properties of FFR and films analyzed. In addition for a given polymer, the nature and level of essential oil are the determinants built respectively for the properties of FFD and films. Generally films designed based on CH or HPMC and essential oils (tea tree, lemon, bergamot) showed significant antimicrobial properties against Escherichia coli, Staphylococcus aureus and Listeria monocytogenes. A complete inhibition of the growth of Gram-negative bacteria, E. coli, was observed for films based on CH or HPMC and tea tree oil. As for the two Gram positive bacteria, L. monocytogenes and S. aureus, the best results were obtained with films of HPMC – tea tree oil and HPMC - bergamot oil respectively.
Volatiles losses during the drying process of films were determined by headspace gas chromatography. Losses increased with the amount of essential oil. The phenomenon of diffusion of essential oils incorporated into films to food is a complex mechanism dependent on several factors such as film structure and polarity, solubility of food simulant and migrant. Results showed that diffusion of limonene, the major component of bergamot essential oil, is higher in ethanol 95%. A linear relationship was observed between the values of diffusion coefficients in ethanol 95% and amount of essential oil in chitosan film. For a given essential oil level, diffusion coefficient decreases with increasing film thickness.
Finally, some of the FFD studied were applied in grapes (cv. Moscatel). The coatings accounted for significant changes in some physicochemical properties of fruit such as weight losses and firmness. The best results were obtained with CH coating enriched with bergamot oil; they showed significant antimicrobial properties, barrier effect against water losses and interesting reduction in respiratory rate.